1. Field of the Invention
The present invention relates to a reclining device for use in a vehicle seat, which is operable to adjust the angle of inclination of a seat back with respect to a seat cushion of the seat.
2. Description of Prior Art
Adjustment of a reclining device in a vehicle seat is effected through locking and unlocking operation between a movable upper arm and a stationary lower base arm thereof so that a seat back fixed on the movable upper arm may be adjustably inclined relative to a seat cushion to which the base arm is fixed, in order that a passenger on the seat can take a proper seating posture. One of the locking mechanisms in this reclining device is known from the Japanese Laid-Open Patent Pub. no. 60-135338. Referring to FIGS. 1(A) and 1(B), this type of locking mechanism uses an inwardly toothed lock portion (24') formed in a stationary lower base arm (12') of reclining device, which is fixed to a seat cushion (not shown), and a movable gear block member (25') having an outwardly toothed portion (25'a), which is movably provided at an upper movable arm (14') of same reclining device, the upper movable arm (14') being fixed to a seat back (not shown).
The upper arm (14') is rotatable about a shaft (16') relative to the base arm (12'). Operation of a cam (34') provided on the shaft (16') causes the gear block member (25') to move rectilinearly along and between two guide plates (G)(G) fixed to the upper arm (14') in a diametrical direction towards and away from the axis of shaft (16') so that the outwardly toothed portion (25'a) of gear block member (25') may be brought in meshed engagement with the inwardly toothed portion (24'), and thus, the upper arm (14') (seat back) can be locked at a selected point with respect to the lower arm (12') (seat cushion).
However, in this prior art, to insure smooth sliding movement of the gear block member (25'), a clearance (R) is provided between the guide plate (G) and gear block member (25'), and the cam (34') contacts and supports a small local part of the gear block member (25'). These factors may result in the gear block member (25') being inclined on such small contact point of cam (34') within both lateral clearances (R) (R) given on the opposite sides of gear block member (25'), as shown in FIG. 1(B), when a great force (F) is applied to both mutually meshed inwardly and outwardly toothed portions (24')(25'a) respectively of the base arm (12') and gear block member (25'). As a consequence of such inclination, the movable gear block member (25') is not completely and evenly meshed with the inwardly portion (24') due to the creation of meshed and non-meshed parts (X)(Y) between those two toothed portions (24') (25'a), as in FIG. 1(B), and a load is intensively exerted on the meshed part (X), which reduces a strength of both toothed portions (24')(25'a). Further, although the clearance (R) is designed to a minimum degree, it is not only difficult technically and cost-wise to minimize such clearance (R) with a precision during a mass-production assembling process, but also it is the matter of fact that even a slight inclination of the gear block member (25') is magnified through the concurrent inclination of the upper arm (14') and transmitted to a passenger on the seat as an appreciable inclination of a seat back fixed to the upper arm (14'), thus resulting in a substantial unstable wobbling of the seat back and making the passenger uneasy and uncomfortable therewith.